Mass separators



' Feb. 17, 1959 F. OPPENHEVIMER ET A 2,374,295

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MASS SEPARATORS Filed Feb. 4. 1946 8 Sheets-Sheet 4 v INVENTORS FrankOpperI/Ie/Mer Byjames M52 Feb. 17, 1959 F, OPPENHEIMER 'ET'AL 2,874,295

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Feb. 17, 1959 MASS SEPARATORS 8 Sheets-Sheet 7 Filed Feb.. 4, 1946f'r-arz OppenAe/nver pyJamgs 1415a Feb; 17, 1959 OPPENHEIMER ETAL2,874,295

IL I I Y I I, I I I I 1 I I I I I I I I I I I I I I I l I I INVENTORSFran/ Oppen/e/fnr BY/am as M 52 Ernest 0. Lawrence.

United States Pate MASS SEPARATORS Frank Oppenheimer and James W. Bell,Berkeley, Calif.,

assignors to the United States'of America as represented by the UnitedStates Atomic Energy Commission Application February 4, 1946, Serial No.645,465

15 Claims. (Cl. 25041.9)

This invention relates to calutrons and more particularly to an ionsource for mass separators, which source is adapted to project a beam ofhigh-velocity ions into a magnetic field.

Calutrons of the general type referred to are described in U. S. PatentNo. 2,709,222, issued May 24, 1955, to

These devices are adapted to separate commercial quantities of materialsthat differ from each other in certain properties, particularly wherethe materials differ in mass. In practice, the materials are reduced toa very small size such as molecular or atomic particles, are ionizedpreferably with like charges, and projected into a magnetic field. Ifthe energies of the two particles are substantially equal, the heavierparticles will describe a circular path of greater radius than thelighter particles, and if suitable collectors are interposed in thecircular paths, the ions may be collected, deionized, and a quantity ofthe material realized that is considerably separated from material ofdifferent mass as compared to the original heterogeneous charge. Thesemass separators are particularly useful for separating isotopes of agiven element, and in practice have been employed to separate isotopesof uranium, particularly the isotope U from the isotope U The mostgeneral technique of operation of these calutrons is substantiallyembodied in the design and mode of operation of the present ion source.The desired metallic element is converted to a salt which may bevaporized at a convenient temperature, and when the isotopes of uraniumare to be separated, it is preferable to change the metal element intochloride or fluoride salts path according to the strength of themagnetic field. The ions, being positively charged particles, areattracted toward the negatively charged electrode and pass through theaperture therein to describe the circular path just referred to. Theheavier U ions have substantially the same energy as the lighter U ions,resulting in the heavier ions describing the arc of greater radius. Inpractice, a divergent beam is used which appears to originatesubstantially at a point close to the ion exit, and because of theeffect of magnetic focusing upon such a divergent beam, the greatestdistance of separation is realized at the 180 point of travel in thecircular path of the ions. Collectors are accordingly disposed at the180 point, the U ions being received in a collector that is separatefrom that for the U ions. When it is possible to obtain an 'ion beamwherein the initial paths of the ions are parallel to each other, thecollection of course takes place at the 90 point of travel.

The general mode of operation just described is somewhat modified bycertain improvements that are embodied in the present invention butwhich form no part thereof. One ofthese improvements is the use of adecelerating electrode as Well as an accelerating electrode. Theaccelerating electrode ofsuch a structure is held at a negativepotential which would result in a circular ion path of much greaterradius than desired, and accordingly an apertured decelerating electrodeis placed closely adjacent to the accelerating electrode so as to reducethe energy of the ion particles passing therethrough, causing the ionsto take a path of the desired radius.

. The purpose of this increased accelerating voltage is to to realize amuch lower vaporizing temperature than that p of the metal. The desiredsalt of the element is placed in a container which is inserted in areservoir or furnace chamber of the ion source. The entire ion sourcemechanism is then placed Within a vacuum envelope which is positionedwithin a magnetic field. When a suitable vacuum is obtained in thevacuum envelope, such as a pressure of 10- to 10- mm. of mercury, heaterelements of the reservoir are operated, vaporizing the salt, which vaporis directed into an ionizing chamber. The ionizing medium is an arcaligned with the magnetic field and the vapor'must pass through the arebefore it can reach the exit opening of the ionizing or are chamber. Theare is not diflicult to strike because of the fact that the charge vaporpresent raises the pressure of the arc chamber considerably above thatof the vacuum tank pressure just mentioned. The electron stream of thearc bombards the molecules of metal salt, breaking them into parts, andin the case of uranium chlorides, a negative chlorine ion is formed anda positive uranium ion is formed, the majority of the uranium ions beingsingly charged.

An apertured accelerating electrode is placed outside of the ion exitopening and is held at a high negative potential, which will cause thepositive ions to be accelerated and thereafter they describe a suitablecircular obtain a greater number of ions from the arc chamber, since thenumber of ions withdrawn is dependent upon the negative voltage of theaccelerating electrode. Thus, the use of accelerating and deceleratingelectrodes in an ion source results in a much larger ion beam having thesame radius, or a smaller radius for the same size ion beam than hadbeen produced prior to this improvement.

A structural feature of considerable importance is also embodied in thepresent invention and in connection with which certain aspects of theinvention find employment. This feature is the use of an ion generator(including the arc block) that is insulated from the supportingstructure of the vacuum envelope, and the operation of the ion generatorat a positive potential with respect thereto. In considering thisfeature it will be realized that an ion source is preferably operated ina vacuum tank that is maintained at ground potential, since this insuresthe greatest safety for the operators of the equipment. The iongenerator which is attached to the inside of the tank may be operated atthe same potential as the tank itself,

in which case the accelerating electrode must be negative withrespect tothe tank and the ion generator so as to create an accelerating electricfield for the ions. In such a structure, however, there'will be anelectric field from the electrode structure to the tank, and after theions pass through the apertured accelerating electrode they willencounter this electric field which will now be in the opposite senseand cause deceleration of the ions. This undesired result is eliminatedby enclosing the area traversedby the ions in a metal tube held at thesame potential as the last electrode in the electrode structure.

The collector is also maintained at a similar potential. The ions insuch a case travel along a path that is completely free of electricfields, the electric fields then being established between thepath-enclosing tube and the vacuum tank.

between this electrode and the tank to perturb the paths of travel ofthe ions. When this last accelerating electrode is at ground potential,the ion generator must necessarily be at a potential that is positivewith respect thereto so that there will be a negative electric field towithdraw the ions from the arc block and accelerate them. Whenaccelerating and decelerating electrodes are used, the ion generator isheld at a potential positive with respect to ground, the acceleratingelectrode is held at a potential negative with respect to ground, andthe decelerating electrode is held at ground potential since it is thelast, or exit, electrode.

In the past, the use of ion generators at a positive potential withrespect to the grounded tank, which are referred to as hot iongenerators, has resulted in severe problems of electron bombardment ofthe various parts of the entire source unit, and particularly theinsulators supporting the ion generator. These electrons come fromseveral places about the ion source, for example stray electrons thatmay be knocked out of the arc chamber by heavier particles, electronsfrom gas that may be ionized in the vacuum tank by the travel of theions, and by secondary emission from the accelerating and deceleratingelectrodes after bombardment by the ion beam or the side bands thereof,such as doubly-charged or triply-charged uranium ions or positivechlorine ions. Upon being released, these electrons are subjected to anelectric field about the ion source that is caused by the fact that thetop and bottom walls of the vacuum envelope are at ground and the iongenerator is at a positive potential with respect thereto. Theelectrons, being negatively charged, are attracted toward the iongenerator, but since the entire ion source is in a strong magnetic fieldthey are confined substantially to the lines of magnetic flux in theirtravel. They therefore continue to be accelerated along the magneticfield until they pass the center of this electric field as they near theion generator. The electrons are then decelerated as they approach thetop or bottom of the tank, assuming the magnetic field to be vertical,since these are negative with respect to the ion source. They arestopped at some intermediate point, depending upon the initial strengthof the electric field in which the electron is generated, and begin areverse travel along the magnetic field, due to the fact that the fieldnow accelerates them that had previously decelerated them after arrivingwith some energy.

The electrons thus oscillate up and down in the magnetic field at a ratebelieved to be several thousand times per second. Due to the usualforces involved in a magnetic field, the electrons, while oscillatingvigorously, will begin a slow migration in a clockwise manner about thehot ion source as viewed from above, when the south pole of the magnetis the upper pole. They thus migrate completely around the ion generatorand strike any insulators that are transverse to the magnetic field. Inthis connection it is noted that prior to the present invention, thecommon practice was to support hot ion generators by insulators thatwere transverse to the magnetic field. The oscillating electrons in suchcases struck the insulator, and since the electrons containedconsiderable energy, caused the insulator to become heated at verylocalized points; namely, the nearest edge to the clockwise travel ofthe electrons. This local heating of the insulator caused it to crackand thereupon become useless.

This insulator cracking problem is so severe as to seriously limit theuse of hot ion generators, and accordingly very elaborate shielding hasbeen devised for the protection of these insulators that are transverseto the magnetic field. The present inventiomhowever, avoids the useofany such insulator shielding by a novel insulating structure that avoidsthe effects of electron oscillation, thus prolonging the life of ionsource units and also resulting in much cheaper production costs.Structures which avoid the use of insulator protecting shielding areemployed at two points in the present invention, one in the support ofthe ion generator, and the other in the introduction of the hot (i. e.,positive) leads that are brought through the vacuum envelope to the iongenerator.

As indicated heretofore, the general structure in which the inventionwill be embodied in an ion source for a calutron, wherein the ion sourceis held at a high positive potential, for example 35 kv., theaccelerating electrode is held at a negative potential, for example 15kv., and a decelerating electrode is employed which is held at groundpotential. The entire source unit is supported by the vacuum envelopethrough the medium of a bracket secured to a removable face plate of thevacuum envelope, which bracket forms a supporting platform that isgenerally transverse to the magnetic field. The ion generator is mountedon a pedestal-type insulator supported on the bracket, and the hot leadsare brought into the vacuum envelope through a tubular elbow connectedto the vacuum envelope, having the axis of its outer opening alignedwith the magnetic field at which point a bushing-type insulator isemployed.

A general object of the invention is to provide a simple and reliableion source mechanism for a mass separator.

It is another object of the invention to provide an ion source having asimple and rugged mounting.

Another object of the invention is to provide an ion source having aninsulated ion generator at a positive potential with respect to the,enclosing vacuum tank, that is free from the problem of electronbombardment of the insulator.

Still another object of the invention is to provide an ion source havingan ion generator at a positive potential that has the electrical leadstherefor brought through the vacuum tank by a construction that protectsthe insulator therefor from electron oscillation.

A feature of the invention is the provision of the ion generator with anovel type of heating and temperature control apparatus.

Other'objects, features and advantages of the invention will be apparentin the following description and claims.

The invention will be described with reference to the accompanyingdrawings, in which:

Figure l is an isometric view of the complete source, including theremovable face-plate of the vacuum envelope;

Figure 2 is a schematic view of the principal electrical components ofthe source, wherein the applied voltages are indicated by differenttypes of lines outlining the components;

Figure 3 is an isometric view, partially exploded, of the aperturedaccelerating electrode and its supporting and adjusting structure;

Figure 4 is a plan view in full section of the ion generator, theaccelerating, and the decelerating structure of the source, taken alongthe line 44 of Figure 5;

Figure 5 is an elevation view in full section of the ion source alongthe line 55 of Figure 9, as viewed from its right side, assuming thatthe forward end of the source is the ion exit end;

Figure 6 is an elevation view of the complete source as viewed from itsleft side, the view being similar to that of Figure 2;

Figure 7 is an elevational view of the complete ion source from theright-hand side, partly in section and with portions broken away, butwith the grounded shielding removed;

Figure 8 is a sectional view of the electrical lead assembly to the highpositive ion generator, taken along the line 88 of Figure 7.

Figure 9 is a plan view of the part of the source inside the vacuumenvelope including the removable face plate, supporting bracket, iongenerator, and accelerating and decelerating structure, except that theplate on the top of the ion generator has been broken away in part; and

Figure is an isomeric view of the oil heat transfer tubes for thereservoir and mixing chamber.

The ion source unit is shown in its completely assembled condition inFigure 1. There is illustrated a removable face plate for the vacuumenvelope, to which is secured a supporting bracket 16. The bracket 16 ispreferably cast and provides a supporting platform for the iongenerator, and the accelerating and decelerating electrodes and that isgenerally transverse to the magnetic field, which is vertical withrespect to Figure 1. As a general measure of the size of this particularembodiment of the invention, it is noted that in one operativeembodiment the bracket 16 is roughly about three feet in length and afoot and a half wide. Supported by bracket 16 is an ion generator unit17 that is held at a high positive potential with respect to the faceplate 15 and the supporting bracket 16, which are at ground potential.The ion generator 17 is surrounded about its sides by spaced shielding18, held at ground potential and therefore referred to as grounded orcold shielding. Potential is supplied to the ion generator 17 by hotleads 24 which pass through an aperture 23 in the face plate 15 andthrough an aperture in the grounded shielding 18. A tubular portion ofthe grounded shielding 18 projects into the aperture 23 and surroundsthe hot leads 24. The accelerating electrode is not visible in Figure 1;however, a decelerating electrode 19 does appear in this view. Thisdecelerating electrode 19 is heated electrically, one terminal for theheater supply being a strip 22 Se cured to the forward end of bracket16, the other end being grounded to the decelerating electrode 19, whichis at ground potential. by a water tube 21 of copper or other suitablematerial, laid about its inside edges. All parts of the ion source arepreferably of a nonmagnetic material to prevent local disturbances ofthe magnetic field passing therethrough.

The electrical construction and operation of the entire The supportingbracket 16 is cooled source unit is shown in Figure 2, wherein are shownbottom and top walls 26 and 27 of a vacuum envelope, as Well as the faceplate 15 that completes the vacuum enclosure. The various parts of theion source unit which are at ground potential are indicated by solidlines, the various insulators are indicated by stippled surfaces, theparts of the ion source at a high positive potential are indicated bydash-dot lines, and the parts of the ion source at negative potentialare indicated by broken lina. A schematic power supply 43 is shown whichmay be of any suitable capacity, such as 50 kv. A resistor 44 connectsthe output terminals and at any desired point this resistor may beconnected to ground, as by a lead 48, so that one end of the powersupply 43 is negative with respect to ground and the other end positive.

The ion generator 17 is supported on an insulator 28 of the pedestaltype by means of a T-shaped bracket 29. There is thus provided aphysical clearance between the ion generator 17 and all other parts ofthe ion source. The ion generator 17 is held at a high positivepotential, as indicated by the dash-dot lines, by a lead 34 connectedthereto and passing through the face plate 15 into a tubular elbow 36which 'has a bushing-type insulator 37 secured to its lower end. Thelower end of the bushing insulator 37 is closed by a plate 38, to whicha positive lead 47 from the power supply 43 is connected. A cathodeassembly 33 is also shown in dot-dash lines, inasmuch as this structurevaries from the potential of the ion generator 17 by only a few hundredvolts, and the leads are similarly brought through the elbow tube 36.Also shown in Figure 2 is an accelerating electrode 31 which is suitablyapertured as indicated in Figure 3, so that the ions from the generator17 may pass therethrough. This accelerating electrode is supported ontwo post insulators 32 by an adjustable mechanism more clearlyillustrated in 'Figure 3. A lead 39 for the accelerating electrodepasses through the face plate 15 by means of a transformer-typeinsulator 41, supported on a tubular collar 42 secured 6 to the faceplate 15. A lead 46 connects the outer end of insulator 41 with thenegative terminal of the power supply 43. The decelerating electrode 19is at ground potential, as indicated by the solid lines, and needs noelectrical lead because it is mechanically fastened to the groundedbracket 16, which in turn is secured to the grounded face plate 15.

In operation, positive ions are formed in generator 17 and areaccelerated outwardly therefrom by the negative potential on accelerator31. Thereafter, they pass through the apertured decelerating electrode19 and, still possessing considerable energy, pass into the magneticfield, there to describe their circular paths as previously mentioned.Suitable collectors may be disposed in these paths, the ions deionized,and material collected. It will be noted that the ion generator mountingbracket 29 covers one end of the pedestal-type insulator 28, the otherend of which is secured to the bracket 16. There is thus a simpleelectric field between opposite ends of the insulator 28 that arealigned with the magnetic field, which field does not induce electronoscillation. As will be described in more detail later, there are noparts of the bushing insulator 37 that are not similarly capped by ahigh potential at one end and a different potential at the other withrespect to the magnetic field, thus avoiding electric fields that induceelectron oscillation.

The detailed structure of the accelerating electrode 31 will bedescribed with reference to Figure 3 before proceeding further with thegeneral description of the ion source as a whole. The post insulators 32(one of which is shown in Figure 3) support a metallic strip 51 having arectangular groove 52 cut therein. Fitted within the groove 52 is aright-angle strip 53 having two elongated holes 54 therethrough intowhich are placed screws 56 that are threaded into the strip 51 to securethe two strips together. Slots 57 are formed through the other leg ofthe angle strip 53, through which screws 58 pass to thread into aflatted end 61 of a supporting arm 62 for the accelerating electrode 31.Three screws 59 are threaded into the strip 53 to contact the face ofthe fiatted portion 61 to adjust the position of the support arm 62 inany plane of movement. The screws 59 and 58 are covered by a cap 64 ofsheet metal, secured by screws 66, thus protecting the screw heads fromthe effects of corrosion by the un-ionized vapor that issues from theion generator 17. The supporting arm 62 is spliced to a shank 63 of theelectrode 31, which has an aperture 49 therethrough. The aperturedelectrode 31, together with its shank 63, is preferably milled from asingle piece of carbon, since this material resists corrosion andbombardment more successfully than most metals. The adjusting structurejust described permits adjustment of the accelerating electrode in allthree dimensions in space and in any plane of rotation.

The general description of the ion source is continued with reference toFigures 4 and 5. There it will be noted that the ion generator 17includes a reservoir 71 which is suitably heated, and into which acharge container 72 may be inserted. When a cap 73 of the charge bottleis removed and the charge heated, vapor flows through a nipple 74 into amixing chamber 76, where it is distributed somewhat confined by a doubleknife-edge bafile plate 77. Thereafter, it passes into an arc chamber 78where it is bombarded by the electron stream of an are initiated by anelectron emissive filament 79. The ions and tin-ionized vapor thereafterissue through the arc slit opening 81, the positive ions beingaccelerated by the high negative potential upon the acceleratingelectrode 31. After passing through the apertured electrode 31, the ionsare subjected to a decelerating electric field defined by an aperturedplate 82 having rounded aperture edges and mounted in the deceleratingelectrode structure 19. A decelerating electric field is present due tothe fact that the decelerating electrode 19 is held at ground potential,which is positive with respect to the accelerating electrode 31. Typicalvoltages that may be applied to the electrode structure are a positive35' kv. on the ion generator 17 with respect to ground, a negative kv.on the accelerating electrode 31 with respect to ground, resulting in atotal accelerating field of 50 kv., and a decelerating potential atground resulting in a decelerating field of 15 kv., giving the beam anet energy as though accelerated by a single electrode of kv.

Having now described the principal components and the general mode ofoperation of the source unit embodying the invention, a detaileddescription will now be given referring again to Figures 4 and 5.Passing through the bottom of the supporting bracket 16 are screws 67,which secure the pedestal-type insulator 23, as well as a lower shallowcup 68 that accurately defines the electric field about the lower end ofthe insulator. Placed on the top of the insulator 28 are two spacerplates 69, the larger of which is cooled by a water tube 83. TheT-shaped bracket 29 is secured to the insulator by bolts 84 passingtherethrough and through the spacers 69. The ion generator 17 is securedto the T-shaped bracket 29 by bolts that secure a U-shaped sheet metalportion 86 of the ion generator, the top of which remains open. Thebottom of the U member 86 is closed by a readily removable plate 87which gives access to the reservoir 71 after removal of a reservoirbottom plate S ll. Secured to the forward end of the U member is acasting 38 in which are formed the mixing chamber 76 and the arc chamber73. The mixing chamber 76 is lined by a suitable corrosion-resistingmaterial 89, such as stainless steel. The entire arc chamber and the arcslit geometry is formed of a single piece of carbon 91, this materialbeing chosen because of its corrosion-resisting properties. The arechamber carbon-911 is secured to the casting 88 by two side strips 92,pressing against shoulders therein. The ion exit or are slit opening isdefined by a beveled edge 93 and two stepped grooves 94 on each side.The operation of the ion exit opening lil is assisted by maintaining thearc slit edges at a high temperature. This is accomplished by cutting adeep groove 96 in the outer face of the carbon back toward the arechamber '78. This groove prevents the conduction of heat from the arcslit opening, which heat is derived from the are itself, thusmaintaining the slits at a high temperature which prevents condensationof vapor thereon, resulting in a clean structure at all times.

The heating system for the reservoir 71 and the mixing chamber '75 isalso illustrated in Figures 4 and 5, as Well as in Figure 10. Thissystem consists of tubing appropriately disposed about the reservoir andmixing chamber and through which a heated liquid may be circulatcd, suchas oil. Since this tubing is an integral part of the ion generator, itmust be held at the same positive potential, and the tubing is thereforebrought through the tubular elbow 36 and in fact forms the electricallead also for the ion generator. Referring to Figures 4, 5, and 10, theinner end of the tube through the tubular elbow is capped by an angleblock 97 to which is connected a length of square tubing 93, formed in ahelix to surround the tubular metal piece forming the reservoir 71. Alower end of the helix is led forwardly and then upwardly to the top ofthe arc and mixing chamber casting 88, which has grooves 99 formed ineither side thereof. This end of the tube 98 is there connected to aheader 161 having three tubes 1922 connected thereto, and which fit inthe grooves 99. A lower header 103 is cross-connected to a similarheader104 on the opposite side of casting 38 by a connecting tube 106. Threetubes .197 lead from this lower header to an upper header 138, fromwhence the return conduit 1'99 leads to a junction block 111 (Figure 9)and thence out the tubular elbow 36.

This type of heating system is particularly suitable for uranium isotopemass separators wherein uranium hexare supported by insulated clamps.

. 8 achloride is used as a charge material. This material vaporizes atthe operating pressure at about 90 C., making feasible the use of hotoil. Heating the charge container 72 also melts a thermoplastic sealabout the ferrous cover 73 thereof, whereupon the magnetic field causesthe cover 73 to assume a vertical position permitting the exit of vapor.The tubes 152 and 107 that lie against the arc and mixing chambercasting 88, which may be cast of copper, serve not only to beat thischamber to a desired temperature but also to maintain the temperaturefairly constant. These tubes may even withdraw heat from this casting 88when an external source of heat, such as the arc, raises the casting toa temperature greater than that desired. Temperatures higher than theoperating temperature may result in the decomposition of uraniumhexachloride vapor to uranium tetrachloride, which has a distinctlyhigher vaporizing temperature and would therefore accumulate as a solidin an undesired manner.

The cathode structure for the ion generator is best illustrated inFigures 5 and 9. Two cathode leads 1.1.2 and 113 pass through thetubular elbow 36 and terminate in cathode clamp blocks 114 and 116,respectively, separated by a strip of mica 115. A difference ofpotential of one to ten volts is maintained between these leads 112 and113 to pass current through the U-shaped filament 7? clamped in blocks114 and 116. Inasmuch as considerable heat is evolved when the filament79 is raised to electron-emissive temperatures by the conductivecurrent, the leads 112 and 113 are preferably squirt tubes; that is,each includes concentric tubing through which cooling water may beintroduced and which is exhausted in the space between the two tubes,the inner tube ending a short distance from the end of the outer tube.In this manner the electrical leads 112 and 113 act as water coolingtubes also, keeping the clamp blocks 114 and 116 cooled. The filamentleads 1.12 and 113 Referring to Figure 5, a block 117 is secured by ascrew to the back of the casting 86 and two short post insulators 118are secured thereto, the upper ends of which support securing blocks119. A screw fastens each securing block 119 to its respective cathodeclamp block. A similar insulated supporting mechanism for the cathodeleads is provided at the back wall of the U-shaped ion generator member86, and is generally referred to as the insulator assembly 120. Placedover the filament 79 is a tungsten plate 121 connected to clamp block114, which is preferably the negative of the two blocks. This platecreates an electric field that is negative with respect to-thc electronemission from the filament, preventing a iiow of electrons to the uppercover of the ion generator which would occur in the absence of such aplate.

Referring still to Figtu'e 5, the upper end of the arc chamber '78includes an apertured plate 122, which aperture admits only the mostintense and steady electron emission from the filament The entire carbonarc block structure is electrically positive with respect to thefilament, and acceleration of the bombarding electrons takes placebetween the filament 79 and the apertured plate 122. The electrons enterthe arc chamber, ionize the vapor emanating from the charge bottle 72,and create an are which enhances the ionizing action of the electronstream. An electron bombardment plate 123 is provided in the bottom ofthe arc chamber and acts to stop the electrons of the arc discharge.This plate 123 is preferably inserted in slots in structure defining theion exit 81.

The details of construction of the decelerating electrode are best shownin Figures 1, 4, 5, and 7. Secured to the support bracket 16 is a pairof upright supports 124. The decelerating electrode 19, which ispreferably cast of copper or similar nonmagnetic material, is mountedtherein byscrews 126. The principal electric field of the electrode isdefined by an apertured plate 82* fittedin a slot in casting 19, and maybe' formed of carbon.

Cast into the decelerating electrode, 19 is a pair of resistance heaters127 of the Calrod type, which comprise an inner rod of resistancematerial insulated from an outer tube by a non-conductor such asmagnesium oxide. Current is supplied to the heaters by the strip 22,which is at 80 to 115 volts above ground, and the inner ends of theheaters are grounded to the decelerating electrode structure. A lead 128passing through the face plate 15 connects the strip 22 with a suitablesource of supply.

The details of the structure for introducing the hot leads inside thevacuum envelope are shown best in Figures 7 and 8. Referring to Figure7, it will be noted that the vacuum envelope is placed between magneticpole pieces 129 of a magnet, which is preferably an electromagnet havingan iron core. Although the principal magnetic field is through the iongenerator and the nearby structure, there is also an intense fringingmagnetic field through the tubular elbow 36. The tubular elbow 36 issecured to the face plate 15 by studs passing through an integral flange131. The elbow 36 turns through the desired angle, in this case 90, toalign the axis of the outer opening with the magnetic field. A flange132 is secured to this outer end and an insulator supporting ring issecured thereto which is spaced from the bushing-type insulator 37.Melted sulfur is poured into the space between these two members, andupon cooling expands to form a tight joint securingthe bushing insulatorto the flange 132. Suitable seals 133 are provided to make the 'joint ofthe insulator 37 with the flange 132 airtight. The cover plate'38'issecured to the lower end of the bushing insulator 37 in a similar mannerThe two ends of the insulator cooling tubing 83 pass throughthe-cover'plate 38 by means of a suitable vacuum seal, and oil heatingtubes 134 also pass therethroughand are suitably sealed against airleak. The cathode squirt tubes 112 and 113 also pass therethrough butare suitably insulated from the cover plate 38 and from each other by aninsulator seal 136. The assembly of all three tubes is shown in Figure8, where it will be noted that the oil heating tubes 134 and thefilament squirt tubes 112'and 113 are enclosed by a.

two-piece housing 137, secured together by screws. The insulatoncoolingtube ends 83 have a separate housing 138;

Referring now to Figure 7, it will be noted that the housing 137 aboutthe hot leads that pass through the elbow 36. is at a high positivepotential with respect to the grounded elbow 36, and that a strongmagnetic field traverses both elements. Electrons that find their wayinto this elbow are therefore caused to oscillate as mentionedpreviously along themagnetic field, due to the electric field set up.These electrons tend to migrate toward the outer end of the tube whilestill maintaining their oscillating condition. In the present structure,however, as the electrons migrate past the turn in the tube they areexposed to the positive potential of the coverpla te 38, as well as thatof the hot lead housing 137, with the grounded elbow wall intermediatethe two. This electric field, a negative member between two positivemembers, does not permit electron oscillation, and the electrons willdischarge to the nearest positive member. Thus the electrons dischargeto the housing 137 or the, plate 38, both of which are made of thickmetal and therefore able to withstand local heating. It will be notedthat the bushing-type insulator 37 is'entirely protected frombombardmentby these electrons because it is within the confines of theflange'132 and the plate 38, and since the electrons cannot leave theirpaths as determined by the magnetic field, there is no possibility thatthey will strike this insulaton For this reason, the defects of priorinsulator construction, namely local heating'due tobombardmenbtarecompletely eliminated, and

electrons.

reliable service as well as long life result from this com s'truction.

.The accelerating electrode bushing passing through the face plate 15 isbest shown in Figures 6 and 9. The flanged collar 42 is fastened to theface plate .15, and the insulator 41 of the transformer type is insertedthrough a hole in the face plate and rests upon the flanged collar 42. Asplit clamping ring 139 mechanically secures the insulator 41 to thecollar 42. The accelerating electrode lead 39 is connected to the innerend of the insulator 41 and the power supply lead 46 is connected to theouter end, which end is tight against air leaks in accordance withstandard manufacturing technique. I

As mentioned in connection with the description of Figure 1, the entireion generator 17 is surrounded by a grounded shield 18. The purpose ofthis shielding is to define the limits of the electric field between thegrounded portions of the ion source and the hot portions, the objectbeing to provide as little volume as possible in which the electrons mayoscillate, inasmuch as the oscillating electrons ionize ambient gas andproduce additional electrons. A series of fins and blisters have beendevised for such shielding, the fins projecting outwardly into thisoscillating volume to further limit the volume in local regions andlimit the amplitude of the oscillating The fins are necessarilycomplemented by protruding blisters in the grounded shielding so as tomaintain the physical clearance necessary to prevent electricalbreakdown. Thus there is shown in Figure 7 a forward fin 141, anintermediate dumping fin 142, and a generally circular rear fin 143.These fins are complemented by blisters in the grounded shielding, asshown in Figure 1; namely, the blisters 144, 146, and 147, respectively.This combination of grounded shielding and fin and blister substantiallyreduces the deleterious efiects of oscillating electrons. .Inasmuch asthis structure forms no part of the invention, the operation is notdescribed in any great detail in the present specification.

It will be noted, however, with reference to Figures 5 and 7, that thepedestal-type insulator 28 is surrounded by a generally cylindricalskirt 148 connected indirectly to the T-shaped bracket 29. This skirtinsures that there will be no electrical fields in the region of theinsulator that will in any way tend to give rise to electron oscillationthat could damage the insulator. The skirt 148 is provided withapertures 150 which aid in the outgassing or pumping down operation ofthe entire vacuum envelope. As explained previously, this skirt is notnecessary and all that is required is a plate that intercepts themagnetic field that permeates the insulator.

Referring still to Figure 5, it will be noted that there is an opening149 in the casting 16 under the reservoir and are chamber regions of theion source. This opening permits access to the ion generator, forexample to permit loading of the charge bottle 72 into the reservoir 71,and is normally covered by a metal sheet 151. The upper surface of theion generator is covered by a plate 152 which aids in keeping out theun-ionized vapor that might otherwise condense upon the various partsthereof. A small block 153 is placed in front of the filament betweenthe arc block and the cover plate 152 to eliminate the electric field ofthe accelerating electrode from the filament region, which mightotherwise result in sparking.

In explaining the detailed operation of the ion source, reference isfirst made to Figures 4, 5, and 7. The source unit is charged when it isoutside of the vacuum envelope.

In removing the source, the volts securing the face plate 15 areunscrewed from the remainder of the vacuum envelope including the topand bottom plates 27 and 26, and removed bodily together with the entiresource unit. The entire source unit is then readily accessible for thecharging operation and any other operations to be performed thereon. Incharging, the cover plate 151 garages is then removed from the bottom ofthe supporting bracket 16 and the bottom plate 87 on the reservoir 71 isalso removed. The plate 90 is next unscrewed, which permits the chargecontainer 72 to drop bodily out of the reservoir 71. A new chargecontainer 72 is then inserted which may be filled with a suitablecharge, such as uranium hexachloride, and properly sealed againstmoisture, as noted previously, by the thermoplastic seal about themagnetically removable cover 73. The plates 90, 87, and 151 are nextreplaced, and the unit is ready for operation.

The face plate 15 is next secured to the vacuum envelope and vacuumpumps (not illustrated) are operated to reduce the pressure within theenvelope to a suitable value such as 10* or 10- mm. of mercury. The highpositive voltage is next applied to the ion generator 17 and the highnegative voltage applied to the accelerator electrode 31, thedecelerating electrode 19 remaining at ground potential. Hot oil is nextcirculated through the oil leads 134 into the tubing 98 surrounding thereservoir chamber 71. The heat from the oil vaporizes the charge, whichaction occurs at about 90 C. when the charge is uranium hexachloride.The heat from the oil also melts the thermoplastic seal about the cover73, and thereafter the magnetic field causes the body of the cover to bealigned therewith, opening the charge container 72. Vapor then flowsthrough the reservoir outlet 74 into the mixing chamber 76, andthereafter the vapor is metered past the baffie 77 to enter the arcchamber 78 at a substantially uniform rate along its entire length.

When the vapor is flowing into the arc chamber 78, a suitable potentialsuch as 200 volts is applied to the cathode leads 112 and 113 withrespect to the rest of the ion generator 17. At the same time, adifference of potential is impressed across the cathode leads 112 and113 which may be of the order of two to ten volts to drive a currentthrough the tungsten filament 79, which is heated to a white heat andbecomes electron emissive. The electrons therefrom are acceleratedtoward the collimating plate 122 in the top of the are chamber 78, andpassing through the opening therein strike an arc in the arc chamber 78.The arc thus formed enhances the ionizing properties of the electrondischarge, producing a large number of ions due to bombardment of thevapor, the pressure in the arc chamber 78 being somewhat higher thanthat of the vacuum tank in general, so that an arc is not difficult tostrike.

The arc plasma fills the entire arc chamber 78, and the positive ions onthe surface of the arc plasma in the region of the ion exit opening 81are accelerated toward the accelerating electrode 31 by the electricfield impressed between the electrode 31 and the arc chamber housing 91.The positive ions thereupon attain considerable energy and pass throughthe aperture 49 in the electrode 31, and upon reaching the extreme exitedge thereof encounter the decelerating electric field induced by theground potential on the decelerating electrode 19. This field is definedby the aperture plate 82 in the electrode 19. Thus, the electrodestructure draws out a large number of ions from the arc plasma in thearc chamber 78, due to the high voltage on the accelerating electrode31, the difference of voltage between the arc chamber housing 91 and theelectrode 31 being of the order of 50 kv. Inasmuch as ions of thisenergy would describe too large a radius within the magnetic field, thedecelerating electrode 19 is employed to reduce the energy of the ions,causing them to describe a circular path of the desired radius.

The ionizing and accelerating actions of the ion source give rise tonumerous electrons outside of the arc chamber housing 91. Theseelectrons encounter the electric field. created by the grounded bracket16, the grounded vacuum envelope top 27, and the highly positive. iongenerator 17. The electrons in attempting to discharge on 12 the highlypositive ion generator 17 are attracted thereto but are confined by thestrong magnetic field permeating the ion source to paths aligned withthe magnetic field. They are thus accelerated to an intermediate pointbetween the two grounded members, whereafter they are decelerated asthey approach the relatively negative vacuum envelope portion 27 or therelatively negative support brackets 16. They are then stopped at someintermediate point and accelerated in an opposite direction by the fieldmentioned, resulting in a very rapid oscillation of the electrons aboutthe ion source 17. This electron oscillation is very undesirable,inasmuch as the electrons possess considerable energy, and upon strikingany object within their path will heat it, either melting it or crackingit when it is a nonmetal such as an insulator. The oscillating electronsare preferably confined to as small volume as possible, inasmuch as theyionize the ambient gas within the vacuum envelope, and produceadditional electrons which also assume the deleterious oscillationspreviously mentioned. This oscillating volume is confined by groundedshielding 18, as shown best in Figures 1, 4, and 5. In this connectionit will be noted that the insulator 28 is so disposed, relative to themagnetic field, that it is entirely outside of the paths that anyoscillating electrons may take. This results from the fact that there isa high positive potential on the upper end of the insulator 28 and arelatively negative field on the other end of the insulator 28,resulting in a simple electric field between the opposite ends thereof.Inasmuch as a simple electric field will not result in electronoscillation, none occurs in this region.

The oscillating electrons migrate rearwardly from the right side of thesource and upon reaching the positive lead assembly, strike a splitoscillating field. Some will continue about the ion generator 17, andwill therefore strike and discharge upon the lead housing 137; others ofthe oscillating electrons make their way through the aperture 20 in therear wall of the grounded housing 18, and continue to oscillaterearwardly along the high positive lead assembly 24 and inside of thetubular elbow 36, as best shown in Figure 7. These electrons continue tooscillate because of the oscillation-inducing field set up as previouslymentioned; namely, a positive element 137 between the grounded upper andlower wall portions of the elbow 36, as aligned with the magnetic field.These electrons continue their slow migration rearwardly until they cometo the turn in the elbow 36, whereupon they are faced with a reversedelectric field; namely, a positive lead assembly 137 and the positivecover plate 38 and the intermediate grounded wall member 36 and itsattached flange 132. This electric field stops all oscillations, theelectrons discharging to the plate 38 or the lead assembly 137,whichever is closer. It will be noticed from this construction and fromthe paths taken by the electrons that the bushing-type insulator 37 iscompletely out of the paths of the oscillating electrons, and is neverstruck by them. This avoids the difficulties of prior constructions,wherein insulators were directly in the path of oscillating electrons,resulting in local portions becoming heated which thereupon cracked theinsulators and rendered them useless as a vacuum seal and weakened themmechanically so that they were unfit to support insulator members.

This description has been made with reference to a particular embodimentthereof, but the invention is not limited to this embodiment norotherwise except by the terms of the following claims.

What is claimed is:

1. In a calutron having a vacuum envelope having a removable wallportion, the combination comprising a bracket secured to the inner faceof the removable wall portion and providing a supporting platformgenerally perpendicular to the removable wall, and an element of '13 anion beam forming mechanism securcd to andflsupported by the bracket. I d

2. In a calutron having means for establishing a magnetic field and avacuum envelope positioned therein, the combination comprising aninsulator attached to the inside of the vacuum envelope, and an iongenerator attached to the insulator for operation at a potentialpositivewith respect to the vacuum envelope, the point of attachment of said iongenerator being positioned with respect to the point of attachment ofthe insulator to the vacuum envelope in a direction along the magneticfield so that the ends of the insulator along the magnetic field aresubject to difierent electrical potentials.

3. In a calutron having means establishing a magnetic field and a vacuumenvelope positioned therein, the combination comprising a tube connectedto the outside of the envelope and communicating with the interiorthereof and having an outer opening with an axis aligned with themagnetic field, a bushing type insulator secured to the outer end of thetube and having its axis aligned with the magnetic field, a cover plateon the unsecured end of the bushing insulator, an element insulatedlymounted inside the vacuum envelope, and leads secured to the cover plateand passing through the bushing insulator and the tube for supplyingelectrical potential to the element inside the vacuum envelope.

4. In a calutron having means establishing a magnetic field and a vacuumenvelope positioned therein and having a removable portion, thecombination comprising a bracket secured to the inner face of theremovable wall portion and providing a supporting platform generallyperpendicular to the removable portion, an insulator secured to thebracket, and an ion generator attached to the insulator for operation ata potential positive with respect to the vacuum envelope, the point ofattachment of said ion generator being positioned along the magneticfield with respect to the point of attachment of the insulator to thesupporting bracket, so that the ends of the insulator along the magneticfield are subject to different electrical potentials.

5. In a calutron having means for establishing a magnetic field and avacuum envelope positioned therein, the combination comprising aninsulator attached to the inside of the vacuum envelope, an iongenerator attached to the insulator for operation at a potentialpositive with respect to the vacuum envelope, said ion generatorattached thereto along the magnetic field with respect to the point ofattachment of the insulator to the vacuum envelope, a tube connected tothe outside of the envelope and communicating with the interior thereofand having an outer opening with an axis aligned with the magneticfield, a bushing type insulator secured to the outer end of the tube andhaving its axis aligned with the magnetic field, a cover plate on theunsecured end of the bushing insulator, and leads secured to the coverplate and passing through the bushing insulator and the tube andconnected to the ion generator for supplying electrical potential to theion generator inside the vacuum envelope.

6. In a calutron having means establishing a magnetic field and a vacuumenvelope positioned therein and having a removable wall portion, thecombination comprising a bracket secured to the inner face of theremovable wall portion and providing a supporting platform generallyperpendicular to the removable wall, an ion generator insulatedlysecured to the bracket, -a tube connected to the outside of theremovable wall portion and communicating with the interior of the vacuumenvelope and having an outer opening with an axis aligned with themagnetic field, a bushing type insulator secured to the outer end of thetube and having its axis aligned with the magnetic field, a cover plateon the unsecured end of the bushing insulator, and leads secured to thecover plate and passing through the bushing insulator and the tube forsupplying electrical potential to the ion generator inside the vacuumenvelope.

'7. In a calutron having means establishing a magnetic field and avacuum envelope positioned therein having a removable wall portion, thecombination comprising a bracket secured to the inner face of theremovable wall portion and providing a supporting platform, an insulatorattached to the bracket, an ion generator attached to the insulator foroperation at a potential positive with respect to the bracket and thevacuum envelope, said ion generator disposed along the magnetic fieldwith respect to the point of attachment of the insulator to the supporting bracket so that the ends of the insulator along the magnetic fieldare subject to difierent electrical potentials, a tube connected to theoutside of the removable wall portion and communicating with theinterior of the vacuum envelope and having an outer opening with an axisaligned with the magnetic field, a bushing type insulator secured to theouter end of the tube and having its axis aligned with the magneticfield, a cover plate on the Iunsecuredend of the bushing insulator, andleads secured to the cover, plate and passing through the bushinginsulator and the tube for supplying electrical potential to the iongenerator inside the vacuum envelope.

8. In a calutron having means establishing a magnetic field and a vacuumenvelope disposed therein having a removable plate portion that isaligned with the magnetic field, the combination comprising a bracketsecured to the inside face of the plate and providing a supportingplatform that is generally perpendicular to the magnetic field, and anion beam forming mechanism secured to and supportedby the bracket.

9. In a calutron having means establishing a magnetic field and a vacuumenvelope positioned therein having a removable plate portion that isaligned with the magnetic field, the combination comprising a bracketattached to the inner face of the plate and forming a supportingplatform that is generally transverse to the magnetic field, aninsulator attached to the bracket, an ion generator attached to theinsulator and having its point of attachment to the insulator disposedalong a magnetic field with respect to the point of attachment of theinsulator to the bracket, an elbow tube secured to the outer face of theplate and communicating with the interior of the vacuum envelope andhaving the axis of its outer opening aligned with the magnetic field, abushing type insulator secured to the outer end of the elbow and havingits axis aligned with the magnetic field, a cover plate on the outer endof the insulator, and leads secured to the cover plate and passingthrough the bushing type insulator and the elbow and connected to theion generator.

10. In a calutron having means for establishing a magnetic field and avacuum envelope disposed therein, the combination comprising aninsulator secured to the inside of the envelope, a metal member securedto the insulator and disposed along the magnetic field with respect tothe point of attachment of the insulator to the vacuum envelope, andintersecting all the magnetic field that passes through the insulator,and an ion generator secured to the member for operation at anelectrical potential difierent from that of the vacuum envelope, thearrangement of the member with respect to the insulator creating asimple electric field about the insulator that eliminates theoscillation of charged particles near the insulator.

11. In a calutron having means establishing a magnetic field and avacuum envelope positioned therein, the combination comprising a tubeconnected to the outside of the envelope and communicating with theinterior thereof and having an outer opening with an axis aligned withthe magnetic field, a bushing type insulator secured to the outer end ofthe tube, the inner dimension of the insulator being at least as greatas the inner dimension of the tube outer opening, a cover plate on theunsecured end of the bushing type insulator, and leads secured to thecover plate and passing through the insulator and tube and adapted to beat an electrical potential different from that of the vacuum envelope.

12. In an ion source, the combination comprising an electrode comprisingan insulated support, a right angled member secured to the support witha connection that is adjustable along one of its legs, a flatted shanksecured to the other end of the member in overlapping and spacedrelationship with a connection that is adjustable along the other leg,three screws threaded in the member and contacting the flat of the shankfor adjusting the flat in any plane relative to the right angle member,and an electrode secured to the shank.

13. In an ion source, the combination comprising an ion generatorreservoir comprising a cylindrical tube, and a helix of smaller tubingwrapped around the cylindrical tube, so that a charge bottle may beinserted in the cylindrical tube and a hot fluid circulated in thehelical tube to heat the charge bottle.

14. In an ion generator, the combination comprising means defining areservoir chamber, means defining a mixing chamber communicatingtherewith, means defining an arc chamber adjacent to the, mixing chamberand wherein an arc discharge is adapted to occur, a tube in heattransfer relationship on the walls of the mixing chamber, and a tubepositioned around the reservoir chamber and connected to the mixingchamber tube, so that a fluid of predetermined temperature may beintroduced therein to heat the reservoir, which fluid may be exhaustedthrough the mixing chamber tube to hold the mixing chamber at a desiredtemperature.

15. In an ion source, the combination comprising means defining an arcchamber having a Wall with an ion exit opening therethrough, means forstriking an arc therein, and heat insulating means about the exitopening comprising a slot cut into the wall adjacent the exit opening,so that the heat imparted to the opening edges is not readily conductedaway by the wall and the temperature of the opening edges is maintained.

No references cited.

